Waist Gang Society -- which is endorsed by Khloe, Kim and Kourtney Kardashian -- is facing a class action lawsuit that could cost the company as much as $5 million. In legal documents obtained by ET, the plaintiffs claim that, despite Waist Gang Society advertising its products will "burn fat and control the user's weight," they have "no effect on fat loss of the user."

"Despite the knowledge that their advertising and marketing are misleading to consumers, defendant continues to advertise, distribute, label, manufacture and market the Products in a misleading and deceptive manner," the plaintiffs allege.

In a letter obtained by ET addressed to the defendant, Sara Hawes, who filed the lawsuit, asks that the company "immediately correct the inaccurate information concerning the purported benefits of the products and refund the cost of the products to all purchasers throughout the state of California," including herself.

The Kardashian clan does not appear to have pulled their endorsement of the company.

Just over a month ago, Khloe Instagrammed that her waist trainer was a "secret weapon," writing: "My workout routine has fallen off due to my crazy work schedule but thank goodness for @premadonna87 and @waistgangsociety!! This company is so dope."

Kim has not been seen wearing her waist trainer since before her pregnancy, but did Instagram about Waist Gang Society a little over five months ago. "#TBT saw this collage online and not gonna lie...can't wait to get back here!!!!" she wrote. "I'm coming for you soon @premadonna87 #WaistGangSociety."

The waist training fad has also faced some backlash from the health and fitness world. In an interview with Yahoo Health, internist Holly Phillips, M.D. gave fair warning about the popular products. "Wearing a corset won’t make you lose fat around your waist," she said. "What is a myth is that you can change your bone structure by wearing them. For [adult] women, your bones are formed. You can bruise them and harm them, but you can't change them."